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Re: Lists
*To*: mathgroup at smc.vnet.net
*Subject*: [mg46987] Re: Lists
*From*: astanoff at yahoo.fr (astanoff)
*Date*: Thu, 18 Mar 2004 04:38:03 -0500 (EST)
*References*: <c3bgbb$7pl$1@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
Clément wrote:
> Hello MathGroup,
> I'm french so i don't speak english very well...
> I have resolved an equation. So i have a list of solutions.
> But how can i extract only the reel solutions of this list ?
> thanks
--
Clément,
Zis is ze way I do :
In[1]:=
realSolutions[sol_]:=#[[1]]&/@Select[{#,#//N}&/@sol,FreeQ[#[[2]],Complex]&];
Example (InputForms inserted for readability) :
In[2]:=sol=Solve[x^3-x+1 == 0];
In[3]:=sol//InputForm
Out[3]//InputForm=
{{x -> -(2/(3*(9 - Sqrt[69])))^(1/3) - ((9 - Sqrt[69])/2)^(1/3)/3^(2/3)},
{x -> ((1 + I*Sqrt[3])*((9 - Sqrt[69])/2)^(1/3))/(2*3^(2/3)) +
(1 - I*Sqrt[3])/(2^(2/3)*(3*(9 - Sqrt[69]))^(1/3))},
{x -> ((1 - I*Sqrt[3])*((9 - Sqrt[69])/2)^(1/3))/(2*3^(2/3)) +
(1 + I*Sqrt[3])/(2^(2/3)*(3*(9 - Sqrt[69]))^(1/3))}}
In[4]:=realSolutions[sol]//InputForm
Out[4]//InputForm=
{{x -> -(2/(3*(9 - Sqrt[69])))^(1/3) - ((9 - Sqrt[69])/2)^(1/3)/3^(2/3)}}
--
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